Portable communication devices, such as cellular telephones, personal digital assistants (PDAs), WiFi transceivers, and other communication devices transmit and receive communication signal at various frequencies that correspond to different communication bands and at varying power levels. A power amplifier module, generally comprising one or more amplification stages, is used to transmit the communication signals. A radio frequency (RF) power amplifier system may include multiple amplification stages, and, in some applications, multiple amplification paths. Regardless of the number of amplification stages and amplification paths, an RF power amplifier typically includes a number of switches. The switches can be used to select an amplification path, to select a modulation methodology, to deliver the input signal to the appropriate amplification path and receive the amplified signal from the selected amplification path, and for other applications.
These switches, however, introduce loss. The loss can degrade signal sensitivity and the signal to noise ratio of the portable communication device and can also degrade linearity, efficiency, etc., in the power amplifier circuit by forcing the radio frequency (RF) power amplifier to be over-driven and by causing the power amplifier to operate in a nonlinear operating region. Further, the input and output switches and the power amplifier circuitry may be fabricated on multiple semiconductor dies, thus significantly increasing the size and the overall complexity of the power amplifier circuit.
Therefore, it is desirable to reduce the number of switches associated with a power amplifier circuit.